Thermal energy storage apparatus

ABSTRACT

A thermal energy storage apparatus is disclosed. The apparatus includes a base and fluid flow plates which cooperate with the base to define a cavity; a phase change material contained within the cavity; an extendable extension spring at least partially contained within the phase change material; and end plates which cooperate with the fluid flow plates to define fluid flow channels. Inlet and outlet ports allow for the ingress and egress of a heat exchange fluid into the fluid flow channels. In operation, the extension of the extendable extension spring induces solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy, allowing for the transfer of thermal energy across the fluid flow plates from the phase change material to the heat exchange fluid.

TECHNICAL FIELD

The present disclosure relates to an apparatus for storing and releasing thermal energy.

DESCRIPTION OF THE RELATED ART

Thermal energy is used for space and water heating, among other things. Thermal energy may be generated or liberated through the combustion of biomass or hydrocarbon-based products such as wood, heating oil, propane, or natural gas, for example. Such products are fairly stable and can be stored for fairly long periods of time without degradation or loss of potential thermal energy release. Such products can also be fairly easily transported without significant degradation or loss of potential thermal energy release. These properties allow for combustion and release of thermal energy at a time and location selected for a particular requirement.

It is difficult however, to generate materials that store thermal energy from transient heat sources, such as solar power, for transport and later release of thermal energy. In an example, thermal energy may be collected by a solar thermal system, generated as electric or resistive heat from electricity supplied by photovoltaics or wind turbines, for example, from a ground source heat pump, or from waste heat sources, such as from effluent from a manufacturing, or thermal power plant. Generating biomass or hydrocarbon materials from such sources is difficult and inefficient. Such thermal energy may be stored by heating water or other thermal masses, such as glycol, and may be transported or stored in insulated tanks, for example. However, such storage is only effective for short-term storage as the thermal energy will dissipate to the external environment through conduction or other means. Thus, a hot water tank, as an example, is not effective long term thermal energy storage mechanism, even with thermal insulation.

A useful long term thermal energy storage system is desired. In particular, a long term thermal energy storage system that has the ability to store thermal energy, to transport stored thermal energy from a source to a desired location, and to release such thermal energy at a desired time without significant loss of thermal energy over time, is desired. A solar thermal system with a transportable thermal energy storage system with minimal loss of thermal energy storage, over days or months, could allow for reduced area of solar collectors which could, in turn, reduce the associated cost of the solar collector.

It is known that thermal energy may be stored in certain phase change materials in a supercooled liquid state. Such a phase change material undergoes a phase transition from solid to liquid at an elevated temperature and when cooled, remains stable in a higher energy supercooled liquid state, below the phase transition temperature. Such a phase change material avoids spontaneously reverting to the lower energy solid state, and as such, can maintain thermal energy associated with the phase transition from the supercooled liquid state to the solid state. Salt hydrates with good solidification rates with respect to heat transfer, high latent heats of transition, and suitable transition temperatures exhibit strong supercooling behaviour and are good candidates for a phase change material based thermal energy storage apparatus. Sodium acetate trihydrate (NaCH₃CO₂.3H₂O) is a safe and easily created material that can be supercooled to temperatures up to 108° Kelvin below the liquid-solid phase transition temperature and can be kept supercooled for significant periods of time, exceeding one year, typically beyond the durations required of a stored thermal energy system.

Sodium acetate trihydrate has long been used as for supercooled liquid thermal energy storage in flexible heat packs for ready-to-use localized warming, for use as hand warmers, for example. In such instances, solid sodium acetate trihydrate in excess water is heated above the melting temperature, melted and fully dissolved, and then cooled and stored in a supercooled liquid state. The supercooled liquid sodium acetate trihydrate can then be triggered to solidify, releasing stored thermal energy at a desired time and location. The release of thermal energy in such flexible hard warmer heat packs is typically accomplished by manually flexing a pre-strained metallic flexible disc located inside the heat pack, immersed within the phase change material. The flexible metal disc is typically fitted with grooves that contain a trapped seed crystal of solid sodium acetate trihydrate. When the flexible disc is flexed, the grooves open and exposes the supercooled liquid sodium acetate trihydrate to the trapped seed crystal. The supercooled liquid sodium acetate trihydrate then crystalizes around the seed crystal, and in the process of solidifying, releases stored thermal energy.

Flexible hand warmer packs however, rely upon manual manipulation of the flexible disc to trigger the solidification process. To permit the manipulation of the flexible disc, the hand-warmer packs are typically made of a flexible translucent pouch which allows an operator to locate the flexible disc and then manipulate the flexible disc, through deformation of the flexible pouch. That is, to be manually manipulated, the flexible pouch must be sufficiently translucent, to locate the flexible disc, must be sufficiently small to allow for the external operator to be able to reach the flexible disc, and the pouch must be sufficiently flexible to allow for the flexion of the flexible disc.

Scaling a flexible heat pack to larger applications poses certain problems. The flexible disc typically moves freely within the supercooled sodium acetate trihydrate liquid. A pouch that is too large to allow for external manipulation of the flexible disc would frustrate the ability to manipulate the flexible disc to trigger nucleation and the release of thermal energy. That is, the pouch is limited in size. Secondly, locating the flexible disc within the supercooled liquid makes automation of the manipulation difficult. That is, an operator must visually locate the flexible disc for manipulation. Thirdly, the flexible nature of the pouch, required to allow for manipulation of the flexible disc, makes it difficult to incorporate within a heat exchange system. Fourthly, the pouch construction of flexible heat packs is a poor candidate for optimizing heat transfer rates with an external fluid medium.

SUMMARY

A modular thermal energy storage apparatus can be summarized as having a housing defining a cavity; a phase change material located within the cavity; an extendable extension spring at least partially contained within the phase change material which may exist in a melted or solid state, wherein extension of the extendable extension spring triggers solidification of the phase change material and a release of thermal energy.

A thermal energy storage apparatus can be summarized as including: a base; a first fluid flow plate positioned so as to cooperate with the base to define a cavity; a phase change material which may exist in a melted or solid state, contained within the cavity; a first extendable extension spring at least partially contained within the phase change material; a first end plate positioned so as to cooperate with the first fluid flow plate to define a first fluid flow channel; a first fluid inlet port in fluid communication with the first fluid flow channel for the ingress of a heat exchange fluid into the first fluid flow channel and a first fluid outlet port in fluid communication with the first fluid flow channel for the egress of the heat exchange fluid from the first fluid flow channel; such that extension of the first extendable extension spring induces solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy allowing for the transfer of thermal energy across the first fluid flow plate from the phase change material to the heat exchange fluid in the first fluid flow channel.

A thermal energy storage apparatus can be summarized as including: a base; a first fluid flow plate assembly comprising at least one fluid flow channel positioned so as to cooperate with the base to define a cavity; a phase change material which may exist in a melted or solid state, contained within the cavity; a first extendable extension spring at least partially contained within the phase change material; a first fluid inlet port in fluid communication with the first fluid flow channel for the ingress of a heat exchange fluid into the fluid flow channel and a first fluid outlet port in fluid communication with the fluid flow channel for the egress of the heat exchange fluid from the fluid flow channel; such that extension of the first extendable extension spring induces solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy allowing for the transfer of thermal energy across the fluid flow plate from the phase change material to the heat exchange fluid in the fluid flow channel.

A thermal energy storage apparatus can be summarized as including: a base; a first fluid flow plate and a second fluid flow plate, the first and second fluid flow plates positioned so as to cooperate with the base to define a cavity; a phase change material which may exist in a melted or solid state contained within the cavity; at least one extendable extension spring at least partially contained within the phase change material; a first end plate positioned so as to cooperate with the first fluid flow plate to define a first fluid flow channel; a second end plate positioned so as to cooperate with the second fluid flow plate to define a second fluid flow channel, a first fluid inlet port in fluid communication with the first fluid flow channel for the ingress of a heat exchange fluid into the first fluid flow channel and a first fluid outlet port in fluid communication with the first fluid flow channel for the egress of the heat exchange fluid from the first fluid flow channel; a second fluid inlet port in fluid communication with the second fluid flow channel for the ingress of a heat exchange fluid into the second fluid flow channel and a second fluid outlet port in fluid communication with the second fluid flow channel for the egress of the heat exchange fluid from the second fluid flow channel; such that extension of the first extendable extension spring induces solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy allowing for the transfer of thermal energy from the phase change material across the first fluid flow plate and the second fluid flow plate to the heat exchange fluid in the first fluid flow channel and the second fluid flow channel.

A thermal energy storage apparatus can be summarized as including: at least one base; an at least one fluid flow plate positioned so as to cooperate with the base to define at least one cavity; a phase change material which may exist in a melted or solid state contained within at least one of the at least one cavity; an at least one extendable extension spring at least partially contained within the phase change material; an at least one end plate positioned so as to cooperate with the at least one fluid flow plate to define an at least one first fluid flow channel; an at least one fluid inlet port in fluid communication with the at least one fluid flow channel for the ingress of a heat exchange fluid into the at least one fluid flow channel, and an at least one fluid outlet port in fluid communication with the at least one fluid flow channel for the egress of the heat exchange fluid from the at least one fluid flow channel; such that extension the at least one extendable extension spring induces solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy allowing for the transfer of thermal energy across the at least one fluid flow plate from the phase change material to the heat exchange fluid in the at least one fluid flow channel.

In any of the above implementations, the thermal energy storage apparatus can further include a baffle within the cavity which obstructs the sinking of solid phase change material.

In any of the above implementations, the thermal energy storage apparatus can include at least one baffle oriented substantially vertically in thermal communication with the phase change material and a fluid flow plate.

In any of the above implementations, the cavity can be substantially cylindrical.

In any of the above implementations, the phase change material can comprise or consist of an organic material. In any of the above implementations, the phase change material can comprise or consist of an inorganic material. In any of the above implementations, the phase change material can comprise a combination of both organic and inorganic materials. In any of the above implementations. the phase change material can comprise sodium acetate trihydrate. In any of the above implementations, the phase change material can comprise sodium acetate trihydrate with additional water.

In any of the above implementations, the thermal energy storage apparatus can further include a film disposed between the base and the first fluid flow plate, wherein the film chemically isolates the first fluid flow plate from the phase change material while maintaining thermal conductivity between the first fluid flow plate and the phase change material.

In any of the above implementations, a fluid flow plate can be comprised of aluminum bonded to stainless steel.

In any of the above implementations, a seal can be disposed between a fluid flow plate and the end plate, sealing the fluid flow channel. In any of the above implementations, a seal can be disposed between the fluid flow plate and the base, sealing the cavity.

In any of the above implementations, the base can further comprise at least one port to allow for the extension of extendable extension spring. In any of the above implementations, the base may further comprise at least one port to allow for filling the cavity with the phase change material.

In any of the above implementations, a fluid flow plate can be disposed with at least one flow director. In any of the above implementations, an end plate can be disposed with at least one flow director. In any of the above implementations, the fluid flow plate and the end plate cooperate to define at least one flow director.

In any of the above implementations, the fluid inlet port can traverse a portion of the base before being in fluid communication with the fluid flow channel. In any of the above implementations, the fluid outlet port can traverse a portion of the base after being in fluid communication with the fluid flow channel. In any of the above implementations, the fluid inlet port can traverse a substantial portion of the base before being in fluid communication with the fluid flow channel.

In any of the above implementations, the first fluid inlet port and the second fluid inlet port can be in fluid communication with each other within the base. In any of the above implementations, the first fluid outlet port and the second fluid outlet port can be in fluid communication with each other within the base.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not necessarily drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not necessarily intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.

FIG. 1 is a perspective view of a thermal energy storage apparatus according to at least one illustrated embodiment.

FIG. 2 is a cross-section view of the thermal energy storage apparatus of FIG. 1 from a front side thereof according to at least one illustrated embodiment.

FIG. 3 is a cross-section view of the thermal energy storage apparatus of FIG. 1 from the back side according to one embodiment.

FIG. 4 is a perspective view of a fluid flow plate of the thermal energy storage apparatus of FIG. 1 according to at least one illustrated embodiment.

FIG. 5 is a cross-section view of a thermal energy storage apparatus from a front side thereof according to at least one illustrated embodiment.

FIG. 6A is a cross-section view of a cylindrical thermal energy storage apparatus taken along a longitudinal axis thereof according to at least one illustrated embodiment.

FIG. 6B is a cross-section view of a cylindrical thermal energy storage apparatus taken along a longitudinal axis thereof according to at least another illustrated embodiment.

FIG. 7A is a perspective view of base of a thermal energy storage apparatus, the base fitted with baffles according to at least one illustrated embodiment.

FIG. 7B is a cross-section view of base fitted with baffles of FIG. 7A, according to at least one illustrated embodiment.

FIG. 8 is a cross-section view of a thermal energy storage apparatus from the front side according to at least one illustrated embodiment.

FIG. 9 is a perspective view of a fluid flow plate of a thermal energy storage apparatus, the fluid flow plate having a number of vertically oriented baffles, according to one embodiment.

FIG. 10 is a cross-section view of a stacked thermal energy storage apparatus from the front side according to at least one illustrated embodiment.

DESCRIPTION OF SPECIFIC EMBODIMENTS

In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known materials, structures and methods associated with vehicles have not been shown or described in detail, to avoid unnecessarily obscuring descriptions of the embodiments.

Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

The headings and Abstract provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

FIG. 1 shows a perspective view of a thermal energy storage apparatus 10 according to at least one illustrated embodiment. Thermal energy storage apparatus 10 is shown with base 12. Moving outwardly from base 12, disposed on either side of base 12 may be film 24 a and 24 b. Film 24 a and 24 b may not be required depending on the particular structure and material of manufacture of fluid flow plates 16 a and 16 b, as is explained later in this disclosure. Base 12 and flow plates 16 a and 16 b collectively comprise a housing. Disposed on either side of optional film 24 a and 24 b, if incorporated, are fluid flow plates 16 a and 16 b. Disposed on either side of fluid flow plates 16 a and 16 b may be gaskets or seals 22 a and 22 b. Gaskets or seals 22 a and 22 b may not be required depending on the particular structure and material of manufacture of fluid flow plates 16 a and 16 b and end plates 18 a and 18 b, as is explained later in this disclosure. Disposed on either side of gaskets or seals 22 a and 22 b, if incorporated, are end plates 18 a and 18 b.

FIG. 1 further shows heat exchange fluid inlets 30 a and 30 b to allow for the ingress of a heat exchange fluid into the thermal energy storage apparatus 10. Corresponding heat exchange fluid outlets are described later in this disclosure. FIG. 1 further shows a seal 52 and a rod 46 extended through and sealed by seal 52. FIG. 1 shows port 15 which may be a sealed cap or threated cap, for example, allowing for pouring in phase change material 14 or for the removal of phase change material 14 from cavity 13. FIG. 1 further shows compression fastener(s) 50 which compresses the elements of base 12, film 22A and 22B, fluid flow plates 16A and 16B, gaskets or seals 22A and 22B, and end plates 18A and 18B, forming the basic structure of the thermal energy storage apparatus 10, according to this embodiment. The compression fastener(s) 50 can, for example, take the form of screws and matching threaded receptacles, threaded bolts and complementary nuts, clamps, and/or compression bands (e.g, spring steel bands).

FIG. 2 shows a cross-sectional view of thermal energy storage apparatus 10 according to at least one illustrated embodiment. On either side of base 12 is disposed film 24A and 24B. On either side of film 24 a and 24 b are fluid flow plates 16 a and 16 b.

Base 12 cooperates with fluid flow plate 16 a, with film 24 a optimally disposed between base 12 and fluid flow plate 16 a, and base 12 cooperates with fluid flow plate 16 b, with film 24 b optimally disposed between base 12 and fluid flow plate 16 b, to collectively define cavity 13. Phase change material 14 is disposed in cavity 13. Phase change material 14 may not fill the entirety of cavity 13 leaving a vapour space 13 a above the phase change material 14, accommodating any thermal expansion of the phase change material.

Fluid flow plate 16 a and end plate 18 a cooperate to define a fluid flow channel 20 a. Fluid flow plate 16 a and end plate 18 a may be optimally sealed by gasket or seal 22 a to seal fluid flow channel 20 a. Fluid flow plate 16 b and end plate 18 b cooperate to define fluid flow channel 20 b on the other side of base 12. Fluid flow plate 16 b and end plate 18 b may be optimally sealed by gasket or seal 22 b to seal fluid flow channel 20 b.

Extendable extension spring 40 is located within cavity 13 and at least partially contained within phase change material 14. Extendable extension spring 40 is fixed to base 12 by mechanically engaging a tab 42. At the other end, extendable extension spring 40 engages rod 46. Rod 46 extends through spring port 44, located in the top of base 12, and is collared and otherwise sealed above base 12 by seal 52. Fluid flow plate 16A is in thermal communication with phase change material 14, via film 24 a, where employed, allowing thermal energy to flow between fluid flow plate 16 a and phase change material 14. Fluid flow plate 16 b is in thermal communication with phase change material 14 via film 24 b, where employed, allowing thermal energy to flow between fluid flow plate 16 b and phase change material 14.

Heat exchange fluid inlet 30 a is in fluid communication with fluid flow channel 20 a via base 12 as shown by the dashed lines in FIG. 2. Heat exchange fluid inlet 30 b is in fluid communication with fluid flow channel 20 b via base 12 as shown by the dashed lines in FIG. 2. In another embodiment, heat exchange fluid inlet 30 a may be in fluid communication with fluid flow channel 20 a via end plate 18 a, such that the heat exchange fluid inlet 30 a is accessed from the side of thermal storage apparatus 10 and heat exchange fluid inlet 30 b may be in fluid communication with fluid flow channel 20 b via end plate 18 b, such that the heat exchange fluid inlet 30 b is accessed from the other side of thermal storage apparatus 10. Similarly, heat exchange fluid outlet 32 a may be in fluid communication with fluid flow channel 20 a via end plate 18 a, such that the heat exchange fluid outlet 32 a is accessed from the side of thermal storage apparatus 10 and heat exchange fluid outlet 32 b may be in fluid communication with fluid flow channel 20 b via end plate 18 b, such that the heat exchange fluid outlet 32 b is accessed from the other side of thermal storage apparatus 10.

FIG. 3 is cross-sectional view of the backside of thermal energy storage apparatus 10 according to at least one illustrated embodiment. As was shown in FIG. 2, FIG. 3 shows on either side of base 12 is disposed optional film 24 a and 24 b. On either side of film 24 a and 24 b are fluid flow plates 16 a and 16 b. Base 12 cooperates with fluid flow plate 16 a, with optional film 24 a disposed between base 12 and fluid flow plate 16 a, and base 12 cooperates with fluid flow plate 16 b, with optional film 24 b disposed between base 12 and fluid flow plate 16 b, to collectively define cavity 13. Phase change material 14 is disposed in cavity 13. Phase change material 14 may not fill the entirety of cavity 13 leaving a vapour space 13 a above the phase change material 14. Fluid flow plate 16 a and end plate 18 a define a fluid flow channel 20 a. Fluid flow plate 16 a and end plate 18 a may be sealed by gasket or seal 22 a to seal fluid flow channel 20 a. Fluid flow plate 16 b and end plate 18 b define fluid flow channel 20 b on the other side of base 12. Fluid flow plate 16 b and end plate 18 b may be sealed by gasket or seal 22 b to seal fluid flow channel 20 b. Extendable extension spring 40 is located within cavity 13 and at least partially contained within phase change material 14. Extendable extension spring 40 is fixed to base 12 by mechanically engaging a tab 42. At the other end, extendable extension spring 40 engages rod 46. Rod 46 extends through spring port 44, located in the top of base 12, and collared above base 12 by seal 52. Spring port 44 is sealed by seal 52. Fluid flow plate 16 a is in thermal communication (e.g., thermally conductive path) with phase change material 14 via film 24 a, allowing thermal energy to conductively flow between fluid flow plate 16 a and phase change material 14. Fluid flow plate 16 a is in thermal communication (e.g., thermally conductive path) with phase change material 14 via film 24 a, allowing thermal energy to conductively flow between fluid flow plate 16 b and phase change material 14. FIG. 3 shows heat exchange fluid outlet 32 a. Heat exchange fluid outlet 32 a is in fluid communication with fluid flow channel 20 a via base 12 as shown by the dashed lines in FIG. 3. FIG. 3 also shows heat exchange fluid outlet 32 b. Heat exchange fluid outlet 32 b is in fluid communication with fluid flow channel 20 b via base 12 as shown by the dashed lines in FIG. 3.

Heat exchange fluid inlet 30 a allows for the ingress of a heat exchange material 34 into fluid flow channel 20 a. Heat exchange fluid outlet 32 a allows for the egress of heat exchange material 34 out of fluid flow channel 20 a. Heat exchange fluid inlet 30 b allows for the ingress of a heat exchange material 34 into fluid flow channel 20 b. Heat exchange fluid outlet 32 b allows for the egress of heat exchange material 34 out of fluid flow channel 20 b.

The relative locations of heat exchange fluid inlet 30 a with respect to heat exchange fluid outlet 32 a, and the relative locations of heat exchange fluid inlet 30 b with respect to heat exchange fluid outlet 32 b, may preferably be located diagonally from one another to promote the flow of heat exchange fluid across the bulk of the fluid flow plates 16 a and 16 b. Further, it may be preferable to locate the heat exchange fluid inlets 30 a and 30 b towards the top of thermal energy storage apparatus 10 and heat exchange fluid outlets 32 a and 32 b towards the bottom of thermal energy storage apparatus 10, as is explained later in this disclosure. However, the location of heat exchange fluid inlets and outlets may be positioned elsewhere and/or at other orientations.

Extendable extension spring 40 is configured to be in an unextended conformation or configuration at the resting unactuated or unextended state, for instance with the windings of extendable extension spring 40 in physical contact with one another. It is believed that extendable extension spring 40 in a conformation where the windings of extendable extension spring 40 are in physical contact with one another applies a local pressure that maintains phase change material 14 in the solid state, in isolation from the surrounding bulk phase change material 14, even when heated above the melting temperature. In such a conformation or configuration, extendable extension spring 40 spontaneously contains at least one seed crystal of phase change material 14 in the solid state.

Extendable extension spring 40 may be actuated from a relaxed state or configuration, e.g., in which the windings of extendable extension spring 40 are generally in physical contact with one another, to an extended state or configuration in which at least some of the windings of extendable extension spring 40 contained within phase change material 14 are separated from one another. Extendable extension spring 40 may be actuated manually, or may be actuated with a solenoid or other mechanical or electro-mechanical motor or servo or the like to extend extendable extension spring 40 upon demand.

Thermal energy storage apparatus 10 may be operated in particular states following initial set-up being: a charging state, a storage state, and a discharge state.

In set-up, cavity 13 is filled with phase change material 14 leaving a portion of cavity 13 unfilled so as to reduce the sealing pressure on seal ports, such as spring port 44, and to accommodate thermal expansion of the phase change material 14. FIG. 1 shows port 15 which may be a sealed cap or threated cap, for example, allowing for pouring in phase change material 14 or for the removal of phase change material 14 from cavity 13. Partial filling of cavity 13 with phase change material 14 is not required and complete filling may be selected by a person of ordinary skill in the art, provided thermal storage apparatus 10 is fitted with a means to accommodate an increase in volume of phase change material 14 which may occur through a phase transition. Filling must however, at least partially immerse extendable extension spring 40 in phase change material 14. In set-up, phase change material 14 will be introduced into cavity 13, generally, in a liquid form, but may be introduced in a solid form.

In a charging state, heat exchange fluid inlets 30 a and 30 b are connected to an external source of heat exchange fluid. Heat exchange fluid outlets 32 a and 32 b may be connected to an external sink for heat exchange fluid or may be connected to the external source of heat exchange fluid to form a loop with heat exchange fluid circulating through thermal energy storage apparatus. In a charging state, heat exchange fluid is introduced into the heat exchange fluid inlets 30 a and 30 b which then flows via heat exchange fluid inlets 30A and 30B into fluid flow channels 20 a and 20 b and then out via heat exchange fluid outlets 32 a and 32 b back to the external source or reservoir, or to the external sink. In a charging state, heat exchange fluid is at a higher temperature than phase change material 14. As heat exchange fluid flows through fluid flow channels 20 a and 20 b, it imparts thermal energy to fluid flow plates 16 a and 16 b. As fluid flow plates 16 a and 16 b heat, they will in turn, thermally conductively impart thermal energy to phase change material 14, via film 24 a and 24 b, if such film is disposed between phase change material 14 and fluid flow plates 16 a and 16 b.

In a charging state, heat exchange fluid is at a temperature greater than the melting point of the phase change material 14 such that solid phase change material 14 melts or dissolves to become a liquid solution. Heat exchange fluid may receive its thermal energy from a solar thermal energy harvester, through a waste thermal energy recovery system or other means to heat the heat exchange fluid. Thus, when heated, heat exchange fluid then flows into fluid flow channels 20 a and 20 b, as described above, and, where heat exchange material is at a temperature greater than the temperature of the phase change material 14, thermal energy will flow across the fluid flow plates 16 a and 16 b, and film 24 a and 24 b, if used, to heat phase change material 14. Heat exchange fluid exits thermal storage apparatus 10 via the heat exchange fluid outlets 32 a and 32 b at a lower temperature than upon entering via heat exchange fluid inlets 30 a and 30 b, in a charging state. This process is continued until phase change material 14 is above the melting point of the phase change material 14, such that the phase change material 14 is liquefied, or dissolves, and at a temperature above the melting point of phase change material 14. At this point, flow of heat exchange fluid may be stopped and thermal energy storage apparatus 10 may enter the storage state.

In a charging state, it is preferable to have heat exchange fluid inlets 30 a and 30 b located towards the top of thermal energy storage apparatus 10 and to have heat exchange fluid outlets 32 a and 32 b located towards the bottom of thermal energy storage apparatus 10. Further, it is preferable to have heat exchange fluid inlets 30 a and 30 b located on one end of thermal energy storage apparatus 10 and to have heat exchange fluid outlets 32 a and 32 b located on the other end of thermal energy storage apparatus 10 such that heat exchange fluid enters towards the top front of the fluid flow plates 16 a and 16 b, and then travels generally diagonally downward towards the back of base 12 to achieve convective thermal transfer. However, other locations and/or orientations of heat exchange fluid inlets 30 b and 30 c and outlets 32 a and 32 b may be employed for a particular application. For example, heat exchange fluid inlets 30 a and 30 b may be located on the side of thermal energy storage apparatus 10 such that the heat exchange fluid inlets 30 a and 30 b run through end plates 18 a and 18 b. However, other locations and/or orientations of heat exchange fluid inlets 30 a and 30 b and outlets 32 a and 32 b may be employed for a particular application. Similarly, heat exchange fluid outlets 32 a and 32 b may be located on the side of thermal energy storage apparatus 10 such that the heat exchange fluid outlets 32 a and 32 b run through end plates 18 a and 18 b. With heat exchange fluid inlets 30 a and 30 b located towards the top and towards one side (front for example) of thermal energy storage apparatus 10 and heat exchange fluid outlets 32 a and 32 b located towards the opposite diagonal, towards the bottom and towards the back, for example, thermal energy from warmer heat exchange fluid entering heat exchange fluid inlets 30 a and 30 b at the top of thermal energy storage apparatus 10 will be imparted to the upper portion of phase change material 14. A convection current will be set up within phase change material 14 such that as colder, molten phase change material is heated, it will rise. The net effect is that there will; be a current of phase change material rising to the top, heating as it rises, and a current of heat exchange fluid flowing towards the bottom, cooling as it descends as it imparts thermal energy to the thermal energy storage apparatus 10. This countercurrent is desirable in heat exchange systems to created greater heat transfer.

When transitioning from the completion of the charging state to a storage state, phase change material 14 may then permitted to cool and, given its nature, phase change material 14 will enter a supercooled state, below the freezing point of phase change material 14. Once phase change material 14 is in a supercooled state, thermal energy storage apparatus 10 may be stored for extended periods of time exceeding one year and may be transported for discharge in a location different from the charging location, if desired.

In a storage state, thermal energy storage apparatus 10 may be disconnected from the external source of heated heat exchange fluid, and the heat exchange fluid inlets 30 a and 30 b and outlets 32 a and 32 b may be disconnected from the external source, if desired. Heat exchange fluid may also be evacuated from the fluid flow channels 20 a and 20 b, if desired, or may remain in fluid flow channels 20 a and 20 b.

The discharge state is initiated when it is desired that thermal energy storage apparatus 10 release stored thermal energy. The discharge of thermal energy occurs when phase change material 14, maintained in a supercooled liquid state, is triggered to enter a solid state. Before triggering phase change material 14 in a supercooled liquid state to enter a solid state, heat exchange fluid should be introduced into flow channels 20 a and 20 b, if previously empty, and heat exchange fluid inlets 30 a and 30 b should be connected to a source of heat exchange fluid, and heat exchange fluid outlets 32 a and 32 b should be connected to a sink of heat exchange fluid, such that heat exchange fluid can impart thermal energy to the thermal mass sought to be heated. The discharge of thermal energy occurs when phase change material 14, in a supercooled liquid state, is triggered to enter a solid state. At a discharge time, extendable extension spring 40 is extended either by manually pulling on extendable extension spring 40 to extend it, through seal 52 directly, or via rod 46 or by having extended extendable extension spring 40 by operation of solenoid or other mechanical/electromechanical means. It has been found that when extendable extension spring 40 located within phase change material 14, in a supercooled liquid state, is extended phase change material 14 is triggered to enter a solid state. It is believed that the local environment contained between the windings of extendable extension spring 40 in an unextended conformation maintains or contains phase change material 14 in a solid state. When extendable extension spring 40 is extended, the phase change material 14 in a solid state contained between the windings of extendable extension spring 40 is open to the bulk phase change material 14 in the supercooled liquid state and presents as a seed crystal upon which phase change material 14 in the supercooled liquid state crystalizes and solidifies. As phase change material 14 transitions from the supercooled liquid state to a solid state, thermal energy is released. Heat exchange fluid in fluid flow channels 20 a and 20 b, at a temperature below the temperature of phase change material 14 which releases thermal energy through solidification will receive thermal energy by thermal conduction from phase change material 14 across fluid flow plates 16 a and 16 b and film 24 a and 24 b, if used. Heat exchange fluid may then be pumped or fed or otherwise motivated from fluid flow channels 20 a and 20 b out of thermal energy storage apparatus 10 via heat exchange fluid outlets 32 a and 32 b to an external sink desired to be heated. Heat exchange fluid may be reintroduced into fluid flow channels 20 a and 20 b via heat exchange fluid inlets 30 a and 30 b to replace heat exchange fluid pumped or fed or otherwise motivated out of fluid flow channels 20 a and 20 b. A loop of heat exchange fluid may be used to feed into fluid flow channels 20 a and 20 b via heat exchange fluid inlets 30 a and 30 b and out of fluid flow channels 20 a and 20 b via heat exchange fluid outlets 32 a and 32 b. This process may continue until thermal equilibrium is reached. Thermal energy storage apparatus 10 may then be placed back into a charging state, or may be stored in the discharged state, if desired.

The system can be operated in reverse if desired and the direction of flow of heat exchange fluid may be switched based on whether the system is in a charging state or discharge state. For example, in a charging state, heat exchange fluid may enter at heat exchange fluid inlets 30 a and 30 b and may exit at heat exchange fluid outlets 32A and 32B. If desired, external plumbing may be manipulated or a flow direction valve or pump may be switched so that in a discharge state, heat exchange fluid may enter at heat exchange fluid outlets 32 a and 32 b and may exit at heat exchange fluid inlets 30 a and 30 b.

Materials and method of manufacture of thermal energy storage apparatus 10 can be selected by a person of ordinary skill in the art for a particular size, volume, type of phase change material, type of heat exchange fluid, and other aspects of a particular application.

In one embodiment, phase change material 14 is comprised of sodium acetate trihydrate, with or without additional water, which has some corrosive properties as against steel or other materials. Sodium acetate trihydrate may itself not be properly classified as organic or inorganic but may be classified as comprised of organic and inorganic materials. Other possible phase change materials include organic or inorganic materials that melt in the operational temperature range and supercool or can be made to supercool and include salt hydrate inorganic phase change materials and sugar alcohol phase change material, such as xylotol, erithritol, for example. An appropriate phase change material may only be selected by a person of ordinary skill in the art.

Base 12 may be constructed from a material that has sufficient mechanical properties to ensure the structural integrity of base 12 and thermal storage apparatus 10 as a whole. Base 12 may also be manufactured from a material that has desired thermal properties and desired chemical properties. Base 12 may be manufactured from plastic such as cast and machined polypropylene. Plastic, such as polypropylene, has good mechanical properties that allows for rigid construction, when sufficiently thick, and has good chemical properties to avoid corrosion when exposed to phase change material 14. Polypropylene also has low thermal conductivity which may be preferable as it is preferentially desired for thermal energy to flow between phase change material 14 and heat exchange material located in fluid flow channels 20 a and 20 b, across fluid flow plates 16A and 16B. Base 12 may be made of more than one material, such steel which has good mechanical properties, partially or fully encased in polypropylene, for example, to achieve the net desired properties of base 12 as a whole. The materials and method of manufacture base 12 may be selected by the person of ordinary skill in the art for a particular application.

When used, in a particular embodiment, film 24 a and 24 b may be a metalized film, such as a film composed of mylar/aluminum/polyethylene. A metalized mylar film 24 provides a chemical barrier between phase change material 14 and fluid flow plates 16 b and 16 b while maintaining thermal conductivity between phase change material 14 and fluid flow plates 16 a and 16 b. Film 24 a and 24 b and may also serve as a gasket or seal to seal cavity 13 between base 12 and fluid flow plates 16 a and 16 b. The materials and method of manufacture for film 24 a and 24 b may be selected by the person of ordinary skill in the art for a particular application.

Fluid flow plates 16 a and 16 b may be constructed out of materials which have good thermal conductivity and good mechanical rigidity. Fluid flow plates 16 a and 16 b may be constructed from cast or machined aluminum alloy, such as a 6061 alloy. Fluid flow plates 16 a and 16 b may also be constructed from cast or machined steel or stainless steel, for example. As noted above, film 24 a and 24 b provides a chemical barrier between phase change material 14 and fluid flow plates 16 a and 16 b. However, where phase change material 14 is not corrosive to fluid flow plates 16 a and 16 b, film 24 a and 24 b may not be required. Alternatively, where phase change material 14 is corrosive to fluid flow plates 16 a and 16 b, film 24 a and 24 b may not be required, if fluid flow plates 16 a and 16 b are coated with a thermally conductive coating which renders fluid flow plates 16 a and 16 b chemically resistant to corrosion caused by phase change material 14. Fluid flow plates 16 a and 16 b may otherwise be bonded or laminated with a film to seal fluid flow plates 16 a and 16 b from phase change material 14. If a film 24 a or 24 b is not used, a gasket or seal may still be required to ensure cavity 13 does not leak to the external environment. Fluid flow plates 16 a and 16 b may be manufactured from a bonded aluminum and 302/304 stainless steel plate, for example, with the stainless steel side exposed to the phase change material 14. A thin layer of stainless steel provides corrosion resistance and thermal conductivity to the aluminum layer. Further, aluminium is less expensive than stainless steel, and a bonded aluminum stainless steel fluid flow plate may be desirable over a full stainless steel plate. Bonding of metals may be produced in a manner as is known by a person of ordinary skill in the art, including processes in the art used in the manufacture of metal stovetop cookware. The materials and method of manufacture for fluid flow plates 16 a and 16 b can be selected by the person of ordinary skill in the art for a particular application.

End plates 18 a and 18 b may be constructed out of materials which have good mechanical rigidity and low thermal conductivity, so as to avoid conduction of thermal energy to the surrounding environment. End plates 18 a and 18 b may be constructed from polypropylene, for example. To increase the mechanical properties of the polypropylene, for a given thickness, end plates 18 a and 18 b may be made of plastic encased or coated steel, or aluminum, for example, or may be constructed in a layered manner, such as a sandwich or laminate of plastic and steel. Such a combination would allow for the polypropylene side to face fluid flow channels 20 a and 20 b, which would allow the low thermal conductively of the plastic to avoid thermal conduction to a steel or other metal back layer which has good mechanical properties, to achieve the net desired properties of the end plates 18 a and 18 b as a whole. End plates 18 a and 18 b may be made of the same metals as disclosed in respect of the fluid flow plates 16 a and 16 b above, but to reduce thermal leakage to the surrounding environment, should preferably be insulated on the outside using insulation such as ethylene propylene diene monomer foam, as an example. The materials and method of manufacture of end plates 18 a and 18 b may be selected by the person of ordinary skill in the art for a particular application.

Extendable extension spring 40 is configured to be in an unextended conformation at the resting unactuated state such that the windings of extendable extension spring 40 are in physical contact with one another. The material for extendable extension spring 40 may selected from materials that have appropriate spring constant and minimum load (pre-stressed) to be actuatable by a solenoid or servo selected for thermal energy storage apparatus 10, and have appropriate windings, diameter, and pre-stressing to allow for retention of a seed crystal of phase change material 14 in an unextended state. Extendable extension spring 40 with elevated minimum load and elevated spring constant is preferred for applications involving the transportation of the thermal energy storage apparatus 10, giving the extendable extension spring 40 resistance to flexure caused by transportation shock and therefore resistance to risks of unintended solidification trigger during transport. For example, extendable extension spring 40 may constructed from 300 grade stainless steel, and may be commercially purchased as item #94135K36 from McMaster-Carr, Aurora, Ohio. A person of ordinary skill in the art may select the material for extendable extension spring 40 for a particular application, but suitable materials include type 300 series stainless steels and corrosion resistant nickel alloys including incoloy, hastaloy, for example.

The combination of end plate 18 a, gasket or sealant 22 b, fluid flow plate 16 b, film 24 b, and base 12 on one side, and on the other side, base 12, film 24 a, fluid flow plate 16 a, gasket or sealant 22 a, and end plate 18 a are held together under compression through one or more compression fasteners 50. Compression fasteners 50 may be a series of through bolts which engage or penetrate the perimeter of base 12, fluid flow plates 16 a and 16 b, and end plate 18 a and 18 b, and other elements, as may be required, which are then secured with nuts to apply a general compression force across the elements, as shown in FIG. 1 (where only one instance of compression fastener 50 is called out for clarity). Alternatively, bands (e.g., metal band, spring steel band) may circumscribe thermal energy storage apparatus 10 to apply a general compression force across the respective elements of thermal storage apparatus 10. As another example, in another example, guiding rods or other means may be employed to line up the various elements of thermal storage apparatus 10 and thermal storage apparatus 10 may be compressed and secured by an external bolted end-plate assembly as is used for commercial plate-and-frame heat exchangers, for example. The materials and method of manufacture of compression fastener(s) 50 may be selected by the person of ordinary skill in the art for a particular application.

FIG. 4 shows a fluid flow plate 16 a according to at least one illustrated embodiment. FIG. 4 shows fluid flow plate 16 a with fluid outlet 54 and fluid inlet 58 with flow directors 34 machined, molded or cast, or set by any suitable means, into the surface of fluid flow channel 20 a. Fluid flow channel 20 a is defined by the cooperation of fluid flow plate 16 a and end plate 18 a (not shown in FIG. 4). Fluid flow plate 16 b, in one embodiment, as shown in FIGS. 1, 2, and 3 may be a mirror image of fluid flow plate 16 a, shown in FIG. 4. As shown in FIG. 1, compression fastener(s) 50 can include a series of through bolts. To allow for such through bolts, fluid flow plate 16 a has a series of perimeter positioned holes 56 drilled or otherwise disposed in fluid flow plate 16 a, such that the threaded action of nuts on one or more end of such through bolts will apply a compression force to the particular elements of the thermal energy storage apparatus 10. The nuts and ends of through bolts are depicted in FIG. 1 as compression fastener(s) 50.

Flow directors 34 (FIG. 4) within fluid flow channel 20 a (and fluid flow channel 20 b, not shown) redirect the flow of heat exchange fluid as it flows across the fluid flow plates, 16 a and 16 b, respectively, as heat exchange fluid passes from heat exchange inlet 30 a to heat exchange fluid outlet 32 a or from heat exchange inlet 30 b to heat exchange fluid outlet 32 b (or vice-versa if the system is operated in reverse, if desired) in the case of fluid flow channel 20 b. The flow directors 34 assist in ensuring heat exchange fluid engages with the available surface of fluid flow plate 16 a (and 16 b not shown), enhanced by the additional surface area available on the face or faces of flow directors 34, within fluid flow channels 20 a and 20 b to increase the conduction of thermal energy between phase change material 14 and heat exchange fluid. Flow directors 34 may be diamond-shaped features, as shown in the embodiment in FIG. 4, but may also be selected by a person of ordinary skill in the art given the particular conditions or requirements of a particular system. For example, flow directors 34 may contact end plates 18 a or 18 b such that the heat exchange fluid must pass around flow directors 34. As another example, flow directors 34 may not contact end plates 18 a or 18 b such that the heat exchange fluid may pass around and over flow directors 34. As another example, fluid flow plates 16 a and 16 v may have flow one or more directors that is a channel, are channels, or are channel like which may be continuous or interrupted. A person of ordinary skill in the art may select the nature of any given the particular conditions or requirements of a particular system, including whether laminar flow or turbulent flow is desired, the location of heat exchange fluid inlets 30 a and 30 b, heat exchange fluid outlets 32 a and 32 b, other factors, including the general shape of the thermal energy storage apparatus 10 as a whole. Such flow directors 34 may be features of fluid flow plates 16 a and 16 b, or end plates 20 a and 20 b, or both fluid flow plates 16 a and 16 b and end plates 20 a and 20 b such that the cooperation of fluid flow plates 16 a and 16 b and end plates 20 a and 20 b define flow directors 34.

Rod 46 may be constructed of a simply solid circular cylinder of material with machined or inserted eye hooks, for example, for engaging with extendable extension spring 40 on one end, and with solenoid or actuator on the other end. Rod 46 may preferably be made of material to withstand the chemical or corrosive effects of the phase change 14, although rod 46 may not contact phase change material 14 directly in ordinary operation. The materials and method of manufacture of rod 46 may be selected by the person of ordinary skill in the art for a particular application.

Tab 42 may be constructed of a machined part of base 12 or as an inserted eye hook into base 12, for example, for engaging with extendable extension spring 40 on the bottom end. The materials and method of manufacture of tab 42 may be selected by the person of ordinary skill in the art for a particular application.

Seal 52 may be constructed of a rubber or similar pliable material that may be adhered or otherwise fixed to base 12 on one end, and may be adhered or otherwise fixed to rod 46 on the other end. Seal 52 is preferred to be selected for integrity under pressure (from thermal expansion of phase change material 14) and at elevated temperature, as well as chemical resistance to phase change material 14 vapour and vapour condensate. Seal 52 may be form of a static or moving shaft seals, or a bellows seal such as may be commercially purchased from McMaster-Carr of Aurora, Ohio as SKU 5298K79, and cut to size, as needed, for example. The materials and method of manufacture of seal 52 may be selected by the person of ordinary skill in the art for a particular application.

Optionally, heat exchange fluid inlets 30 a and 30 b may be located in base 12 and may traverse a portion of base 12 before turning and entering fluid flow channels 20 a and 20 v. Similarly, heat exchange fluid outlets 32 a and 32 b may be located in base 12 such that heat exchange fluid exits fluid flow channels 20 a and 20 b and then traverses a portion of base 12 before exiting the thermal energy storage apparatus 10 at heat exchange fluid outlets 32 a and 32 b. As phase change material 14 solidifies, it condenses and becomes denser, as compared to phase change material 14 in the liquid state. In a charging state, thermal energy is supplied to phase change material 14 from heat exchange fluid in fluid flow channels 20 a and 20 b. As phase change material 14 transitions from a solid state to a liquid state, any remaining solid phase change material 14 may sink to the bottom of cavity 13. As such, it may be preferable to apply more thermal energy to the bottom of cavity 13 to liquefy any sinking solid phase change material 14 although such a configuration may lead to concentration of phase change material solute towards the bottom of cavity 13, which may lead to the creation of an inhomogeneous solid phase change material 14, such as anhydrous/hydrous sodium acetate, which may lead to auto-nucleation, which is not desired. To avoid undesirable levels of concentration of solute, a mechanical mixer may be employed, such as a rotating paddle wheel, which may be extant within cavity 13 and operated via a port, for example. As such, configuring base 12 to house heat exchange fluid inlets 30 a and 30 b and heat exchange fluid outlets 32 a and 32 b and configuring base 12 such that heat exchange fluid inlets 30 a and 30 b or heat exchange fluid outlets 32 a and 32 b traverse a lower portion of base 12 before turning to or turning from fluid flow channels 20 a or 20 a would provide additional thermal energy to the bottom of base 12 and the bottom of cavity 13 to heat sunken solid phase change material 14. As such, it may be preferential to configure base 12 so as to have a more thermally conductive bottom portion to allow for the conduction of thermal energy as described above, or that such elements may be positioned towards the upper surface of the bottom of base 12 to improve heat transfer, provided there is sufficient material between such channels and the upper surface of the bottom of base 12 to prevent a leak or rupture at all operating temperatures of thermal storage apparatus 10. It is advantageous for base 12 to be otherwise insulated or insulating to minimize thermal losses to the external environment. Base 12 may be generally circular, square, rectangular, or other shape, selected by a person of ordinary skill in the art.

In one embodiment, thermal energy storage apparatus 10 may be generally configured to remain in the upright orientation shown in FIG. 1. With this orientation, spring ports 44 located on the upper surface of base 12 may only need to be configured to prevent the egress of vapour of phase change material 14, as compared to being configured to prevent the egress of liquid phase change material 14. However, if phase change material 14 substantially fills cavity 13, thermal expansion of phase change material 14 at elevated temperatures may cause phase change material 14 to expand into port 15 or spring ports 44 and seal 52, and such ports may require sealing against pressure from liquid phase change material 14.

Optimally, in at least one embodiment, extendable extension spring 40 may be extended to outside of base 12 by the top portion of extendable extension spring 40 extending through a sealed spring port 44, located in the top of base 12, such that the top of extendable extension spring is engaged and activated to trigger solidification of phase change material 14, removing the need for rod 46.

In at least one embodiment, flow channel 20A may be sealed through a gasket or sealant 22 a such that the fluid flow channel 20 a is sealed from the external environment. Flow channel 20 b may be sealed through a gasket or sealant 22 b such that the fluid flow channel 20 b is sealed from the external environment. In another embodiment, gasket or sealant 22 a and 22 b may not be required if tolerances of fluid flow plate and end plate allow for a leak free joint, or where fluid flow plate is otherwise sealed to end plate or by an adhesive, or by brazing or welding, for example. Suitable materials for gasket or sealant 22 a and 22 b for a particular application may, for example, include silicone rubber, nitril rubber, latex rubber (depending on use with glycol or not), and butyl rubber.

Thermal energy storage apparatus 10 is shown in FIGS. 1, 2, and 3 as a two sided apparatus with a general bilateral symmetry. In another illustrated embodiment, thermal energy storage apparatus 10 may be a one sided apparatus, with fluid flow channel on one side only. FIG. 5 shows a one-sided apparatus in cross section, according to at least one illustrated embodiment. As shown in FIG. 5, base 12 cooperates with fluid flow plate 16 a to define cavity 13 in which phase change material 14 is located. Phase change material 14 may not fill the entirety of cavity 13 leaving a vapour space 13 a above the phase change material 14. Fluid flow plate 16 a and an end plate 18 a define a fluid flow channel 20 a, where fluid flow plate 16 a has sufficient thermal conductivity to be in thermal communication with phase change material 14 and to allow thermal energy to flow between fluid flow plate 16A and phase change material 14. As shown in FIG. 5, fluid flow plate 16 a and end plate 18 a, which define fluid flow channel 20 a, may be sealed through a gasket or sealant 22 a such that the fluid flow channel 20 a is sealed from the external environment. Gasket or sealant 22 a may not be required if tolerances of fluid flow plate 16 a and end plate 18 a allow for a leak free joint. In this embodiment, film 24 a may be optimally disposed between fluid flow plate 16 a and base 12.

The shape of thermal energy storage apparatus 10 may be configured by a person of ordinary skill in the art however, it has been found that a greater surface area of fluid flow plates to volume of cavity ratio allows for greater conduction of thermal energy between phase change material and heat exchange fluid. In at least one illustrated embodiment, thermal energy storage apparatus 10 may be generally cylindrical in shape, including for example, a circular cylinder shape. A cross-section of a circular cylindrical shaped thermal energy storage apparatus 10 is depicted in FIG. 6A. FIG. 6A shows the cylindrical thermal energy storage apparatus 10 with cavity 13, extendable extension spring 40, phase change material 14 within cavity 13, a cylindrical fluid flow plate 16 c and a cylindrical end plate 18 c. The cylindrical fluid flow plate 16 c and a cylindrical end plate 18 c define the cylindrical fluid flow channel 20 c. In this embodiment, base 12 may be comprised of end caps that secure and further cooperate with the above elements to define cavity 13 and fluid flow channel 20 c. Inlets and outlets may be included within such end caps. For example, a base 12 end cap component may be a machined cylindrical block with machined cylindrical channels into which cylindrical fluid flow plate 16 c and a cylindrical end plate 18 c sit or may be cylindrical ridges which abut cylindrical fluid flow plate 16 c and a cylindrical end plate 18 c. The end caps and fluid flow plate 16 c are collectively a housing. Seals may be employed as required.

FIG. 6B shows a cross-section of a thermal energy storage apparatus 10 according to another embodiment. In this embodiment, the cavity is defined by the cylindrical wall fluid flow plate 16 c and the end caps, not shown. In this embodiment, the thermal storage apparatus sits within a bath of heat exchange fluid, such as may be found in a shell and tube heat exchanger.

Thermal storage apparatus 10 may optionally include more than one extendable extension spring 40 placed within cavity 13, each at least partially immursed within phase change material 14. Generally, the more windings of extendable extension springs, which are increased with the number of extendable extension springs within cavity 13, the greater probability that the extension of an extendable extension spring will release a seed crystal of phase change material 14 triggering the solidification of phase change material 14. Further, with more than one extendable extension spring 40 placed within cavity 13, each at least partially submerged within phase change material 14, where each is extended at or near the same time, the greater the speed with which phase change material 14 may release thermal energy as it transitions from a supercooled liquid to a solid.

A thermocouple or thermocouples or other temperature sensors may be introduced into cavity 13, or may be extant within cavity 13 to inform operational systems as to when either thermal equilibrium or supercooling is reached, or when other thresholds are reached, which may trigger the start or cessation of a pump or other mechanism motivating heat transfer material, or may trigger the start or cessation of a mixing element, or for other aspects of operation such as solidification triggering. Such temperature sensors may enter the cavity 13 through base 12, for example, and may be sealed by compression fittings or by other means described herein.

Cavity 13 may be a single cavity, may be comprised of a number of subcavities, or may be a single cavity fitted with baffles. FIG. 7A depicts a perspective view of base 12 fitted with baffles 60 (only one called out for clarity of the figure), without phase change material 14 filled within cavity 13. FIG. 7A shows port 15. FIG. 7A shows holes drilled or otherwise located within base 12 as part of compression fastener(s) or fittings 50, or to permit the passage of bolts, for example. FIG. 7A also shows spring port 44, in this embodiment showing two spring ports 44 for two extendable extension springs (extendable extension springs not shown). Baffles 60 also have ports to allow for the passage of extendable extension spring, not shown, through cavity 13 to engage with tab 42. FIG. 7A also shows base 12, and baffles 60 configured with additional ports or passages 68 to allow for the addition of thermocouples, if desired. FIG. 7A also shows heat exchange fluid inlet 30 a, which then turns within base 12 and is configured to enter the fluid flow channel (not shown) via port 62. Similarly, heat exchange fluid would exit the fluid flow channel via port 64 which would then turn and exit the fluid flow outlet 32 a (not sown in FIG. 7A). In at least one embodiment, the fluid flow inlet may split within base 12 and turn and feed fluid flow channels on both sides of base 12.

FIG. 7B shows a cross sectional view of base 12 fitted with baffles 60 (only one called out for clarity of the figure), without phase change material 14 filled within cavity 13. FIG. 7B shows port 15. FIG. 7B shows holes drilled or otherwise located within base 12 as part of compression fastener(s) or fittings 50, or to permit the passage of bolts, for example. FIG. 7B also shows spring port 44, in this illustrated embodiment showing two spring ports 44 for two extendable extension springs, (extendable extension springs not shown). Baffles 60 also have ports to allow for the passage of extendable extension spring, not shown, through cavity 13 to engage with tab 42. FIG. 7B also shows base 12, and baffles 60 configured with additional ports or passages to allow for the addition of thermocouples, if desired. FIG. 7B also shows heat exchange fluid inlet 30 a, which then turns within base 12 and is configured to enter the fluid flow channel (not shown) via port 62. Similarly, heat exchange fluid would exit the fluid flow channel via port 64 which would then turn and exit the fluid flow outlet 32 a. In at least one embodiment, the fluid flow inlet may split within base 12 and turn and feed fluid flow channels on both sides of base 12. As can be seen in FIG. 7B, baffles 60 do not traverse the entirety of cavity 13, so as to allow for filling of cavity 13 with phase change material via the single port 15. In another embodiment, baffles 60 may traverse cavity 13, but may have holes or apertures to for filling of cavity 13 with phase change material via the single port 15. In another embodiment, baffles 60 may traverse cavity 13 such that cavity 13 effectively becomes a plurality of cavities, each requiring a port for filling, if filling occurs after assembly.

Baffles 60 may be in any conformation, as selected by a person of ordinary skill in the art, provided they have some horizontal component, as compared to the direction of gravity to combat stratification of the phase change material 14 by preventing much of the solid phase change material 14 from sinking to the bottom of the cavity 13 during melting. When arranged vertically, baffles 60 may may assist in the transfer of heat from phase change material 14 to fluid flow plates 16 a and 16 a. Baffles 60 may or may not transverse the entirety of cavity 13, but to permit the filling of the entirety of cavity 13 from a single filling port, baffles should not traverse the entirety of cavity 13, or should be fitted with apertures to permit the flow of phase change material 14 around or through baffles 60. Further, baffles 60 may be fitted with apertures to permit the passage of extendable extension spring 40 through the bulk of phase change material 14. Baffles 60 may also assist heat transfer from the phase change material 14 to fluid flow plates as baffles 60 may be constructed of thermally conductive materials, and sealed or coated as described herein Phase change material 14 may be any material capable of being in a liquid or solid state and capable of being supercooled in a liquid state. Phase change material 14 may be sodium acetate trihydrate with or without additional water, for example, provided the phase transition temperatures and other properties of the phase change material 14 do not exceed the operating temperature limits of the materials of construction of the other elements of the thermal energy storage apparatus 10. The preferable phase change material may be selected by a person of ordinary skill in the art for a particular application based on the teachings herein.

FIG. 8 shows baffles 60 that are in thermal communication with fluid flow plates 16 a or 16 b and with phase change material 14. Only one baffle 60 is called out in FIG. 8, for clarity, and baffles 60 are only shown on one portion of fluid flow plate 16 a, for clarity. However, baffles 60 may be arranged on any part of fluid flow plate 16 a or 16B and may be generally uniformly distributed across such fluid flow plates. Baffles 60 may be arranged generally horizontally, or generally vertically, or at an angle selected by a person of ordinary skill in the art. Generally vertically arranged fins may be preferable as they may be able to be infiltrate the cavity 13 without interfering with extendable extension spring 40 as baffles 60 shown as generally horizontal fins may have to be shorter or have ports to allow for the passage of extendable extension spring 40, or other elements such as a thermocouple, if employed. Baffles 60, for example in the form of thermally conductive fins or pins may be fixed to the cavity-facing sides of the fluid flow plates 16 a or 16 b or may be machined integral elements of fluid flow plates 16 a or 16 b. However, the use of such baffles 62 may make the use of film 24 a or 24 b more difficult to implement. As such, the coated fluid flow plates, as described above, or corrosion resistant fluid flow plates (e.g., stainless steel) sealed to base 12 without the use of film 24 a or 24 b, may be preferable. In another embodiment, thermally conductive material may be distributed throughout cavity 13 such that it is in thermal communication with both phase change material 14 and fluid flow plates fluid flow plate 16 a or 16 b, to enhance the thermal transfer between phase change material and fluid flow plates 16 a or 16 b. Such thermally conductive material may include metallic packing, material, metallic foam or wool, or a graphite composite, for example. Such material may be fixed or abutted to a fluid flow plate to ensure thermal communication, and where loose packing material is selected, for example, then the conductivity is generally determined by the orientation and packing of the material such that there may be at least one pathway of thermal communication from the material to a fluid flow plates, such that the majority of the material is in some manner in thermal communication with the fluid flow plates.

FIG. 9 shows a perspective view of a fluid flow plate 16 a with baffles 60 as vertically oriented fins. FIG. 9 shows the side of fluid flow plate 16 a facing cavity 13. Only one instance if baffles 60 is called out in FIG. 9, for clarity.

FIG. 10 is a cross-section view of a stacked thermal energy storage apparatus from the front side according to one embodiment. FIG. 10 shows a stack configuration of a thermal energy storage apparatus 10, comprised of a plurality of bases (three shown in FIG. 10) with associated fluid flow plates and end plates, to complete a stacked arrangement of unit cells to comprise a stacked thermal energy storage apparatus 10D. Going from left to right, the stacked thermal energy storage apparatus 10D shows end plate 18 a, a fluid flow plate 16 b and base 12. On the right hand side of the left hand base 12, is disposed a fluid flow plate 16 a, a central end plate 18 d and then fluid flow plate 16 b. Continuing on, is another base 12, a fluid flow plate 16 a, a central end plate 18 d, fluid flow plate 16B, base 12, fluid flow plate 16 a and end plate 18 a. The stacked thermal energy storage apparatus 10 d is configured such that the base units share the central end plates 18 d. Also in this configuration, but not shown, compression fastener(s) or fittings 50 may compress the entire stacked thermal energy storage apparatus 10 d with one such compression fastener or fitting. For example, compression fastener or fitting comprised of through bolts would run through the elements listed above and compress the thermal energy storage apparatus 10 d stack. Also shown in FIG. 10 is a single heat exchange inlet port 30 d for each base 12 where heat exchange fluid enters base 12 via heat exchange inlet port 30 d which then traverses a portion of base 12 before turning and entering the fluid flow plates 16 a and 16 b on either side of the particular base 12. Seals and films may be employed in such a stacked thermal energy storage apparatus 10 d, as is described above, but are not shown for clarity. Further, the number of bases within a single stacked thermal energy storage apparatus may be selected by a person of ordinary skill in the art for a particular application. Stacked thermal energy storage apparatus may be configured such that each base unit cell operates independently, where it is preferable that central end plates 18 d are thermally insulating to thermally isolate the adjoining base unit cells or stacked thermal energy storage apparatus may be configured such that the base unit cells operate collectively, where it is not required that central end plates 18 d are thermally insulating. 

1. A thermal energy storage apparatus, comprising: a first housing that forms a first cavity; a first amount of phase change material located in the cavity of the housing, the phase change material which is convertible between a melted state and a solid state; and an extendable extension spring at least partially contained in the first amount of phase change material and operable to trigger a state change of the first amount of phase change material from the melted state to the solid state, and thereby release thermal energy stored in the first amount of phase change material.
 2. The thermal energy storage apparatus of claim 1 wherein first housing comprises: a base; a first fluid flow plate positioned with respect to the base to form the first cavity therebetween a first end plate positioned relative the first fluid flow plate to define a first fluid flow channel; a first fluid inlet port in fluid communication with the first fluid flow channel for the ingress of a heat exchange fluid into the first fluid flow channel; and a first fluid outlet port in fluid communication with the first fluid flow channel for the egress of the heat exchange fluid from the first fluid flow channel; such that extension of the first extendable extension spring induces solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy allowing for the transfer of thermal energy across the first fluid flow plate from the phase change material to the heat exchange fluid in the first fluid flow channel.
 3. The thermal energy storage apparatus of claim 1, further comprising: a second housing that forms a second cavity, the second housing stacked with the first housing; a second amount of phase change material located in the cavity of the housing, the phase change material which is convertible between a melted state and a solid state; and an extendable extension spring at least partially contained in the second amount of phase change material and operable to trigger a state change of the second amount of phase change material from the melted state to the solid state, and thereby release thermal energy stored in the second amount of phase change material.
 4. A thermal energy storage apparatus, comprising: a base; a first fluid flow plate assembly comprising at least one fluid flow channel positioned with respect to the base to define a cavity therebetween; a first fluid inlet port in fluid communication with the first fluid flow channel for the ingress of a heat exchange fluid into the fluid flow channel; a first fluid outlet port in fluid communication with the fluid flow channel for the egress of the heat exchange fluid from the fluid flow channel; a first amount of phase change material located in the cavity, the phase change material which is convertible between a supercooled liquid state and a solid state; and an extendable extension spring at least partially contained in the first amount of phase change material and operable to extend from a first configuration to a second configuration, and in the second configuration trigger a state change of the first amount of phase change material from the supercooled liquid state to the solid state, and thereby release thermal energy stored in the first amount of phase change material wherein the released thermal energy transfers across the fluid flow plate from the phase change material to the heat exchange fluid in the fluid flow channel.
 5. The thermal energy storage apparatus of claim 4 wherein the first fluid flow plate assembly comprises: a first fluid flow plate; a second fluid flow plate, the first and the second fluid flow plates positioned with respect to one another and positioned with respect to the base to define a cavity therebetween; a first end plate positioned with respect to the first fluid flow plate to define a first fluid flow channel therebetween; a second end plate positioned with respect to the second fluid flow plate to define a second fluid flow channel therebetween, a first fluid inlet port in fluid communication with the first fluid flow channel for the ingress of a heat exchange fluid into the first fluid flow channel; a first fluid outlet port in fluid communication with the fluid flow channel for the egress of the heat exchange fluid from the first fluid flow channel; a second fluid inlet port in fluid communication with the second fluid flow channel for the ingress of a heat exchange fluid into the second fluid flow channel; a second fluid outlet port in fluid communication with the second fluid flow channel for the egress of the heat exchange fluid from the second fluid flow channel, and wherein the heat exchange fluid in the first and the second fluid flow channel are thermally coupled to receive at least a portion of the released thermal energy that transfers across the first and the second fluid flow plates from the phase change material.
 6. The thermal energy storage apparatus of claim 4 wherein the first fluid flow plate assembly comprises: at least one fluid flow plate, the at least one fluid flow plate positioned with respect to the base to define at least one cavity; at least one end plate, the at least one end plate positioned with respect to the at least one fluid flow plate to define an one fluid flow channel; at least one fluid inlet port in fluid communication with the at least one fluid flow channel for the ingress of a heat exchange fluid into the at least one fluid flow channel; a least one fluid outlet port in fluid communication with the at least one fluid flow channel for the egress of the heat exchange fluid from the at least one fluid flow channel, and wherein the heat exchange fluid in the at least one fluid flow channel is thermally coupled to receive at least a portion of the released thermal energy that transfers across the at least one fluid flow plate from the phase change material.
 7. The thermal energy storage apparatus of claim 4 wherein the molten state of the phase change material is a supercooled liquid state.
 8. The thermal energy storage apparatus of claim 4, further comprising: at least one baffle within the cavity, wherein the at least one baffle which obstructs the sinking of solid phase change material.
 9. The thermal energy storage apparatus of claim 4 wherein the phase change material is comprised of an organic material.
 10. The thermal energy storage apparatus of claim 4 wherein the phase change material is comprised of an inorganic material.
 11. The thermal energy storage apparatus of claim 4 wherein the phase change material is comprised of inorganic and organic materials.
 12. The thermal energy storage apparatus of claim 4 wherein the phase change material is comprised of sodium acetate trihydrate.
 13. The thermal energy storage apparatus of claim 4, further comprising: a film disposed between the base and the first fluid flow plate, wherein the film chemically isolates the first fluid flow plate from the phase change material while maintaining thermal conductivity between the first fluid flow plate and the phase change material.
 14. The thermal energy storage apparatus of claim 4 wherein the first fluid flow plate is comprised of aluminum bonded to stainless steel.
 15. The thermal energy storage apparatus of claim 4, further comprising: a seal disposed between the first fluid flow plate and the base, sealing the cavity.
 16. The thermal energy storage apparatus of claim 4, further comprising: at least one port that allows for the extension of extendable extension spring.
 17. The thermal energy storage apparatus of claim 4 wherein wherein the base further comprises at least one port to allow for filling the cavity with the phase change material.
 18. The thermal energy storage apparatus of claim 4 wherein the first fluid inlet port traverses a portion of the base before being in fluid communication with the first fluid flow channel.
 19. The thermal energy storage apparatus of claim 4 wherein the first fluid outlet port traverses a portion of the base after being in fluid communication with the first fluid flow channel.
 20. The thermal energy storage apparatus of claim 4 wherein the first fluid inlet port traverses a substantial portion of the base before being in fluid communication with the first fluid flow channel.
 21. The thermal energy storage apparatus of claim 4 wherein the cavity is cylindrical.
 22. The thermal energy storage apparatus of claim 4 wherein the phase change material is inorganic.
 23. The thermal energy storage apparatus of claim 4, further comprising: at least one baffle in thermal communication with the phase change material and the first fluid flow plate.
 24. The thermal energy storage apparatus of claim 4 wherein the first fluid flow plate is disposed with at least one flow director.
 25. The thermal energy storage apparatus of claim 4 wherein the first end plate is disposed with at least one flow director.
 26. The thermal energy storage apparatus of claim 4 wherein the phase change material is comprised of sodium acetate trihydrate with additional water.
 27. The thermal energy storage apparatus of claim 5, further comprising: a seal disposed between the first fluid flow plate and the first end plate, sealing the first fluid flow channel.
 28. The thermal energy storage apparatus of claim 5 wherein the first fluid inlet port and the second fluid inlet port are in fluid communication with each other within the base.
 29. The thermal energy storage apparatus of claim 5 wherein the first fluid outlet port and the second fluid outlet port are in fluid communication with each other within the base.
 30. The thermal energy storage apparatus of claim 5 wherein wherein the first fluid flow plate and first end plate are positioned relative to one another to define at least one flow director. 